An assisted direct start (ADS) engine may use a number of factors to determine when to shut down and restart the engine to achieve the goal of reducing fuel consumption and emissions while the vehicle is stationary. Typically, the engine is shut down when wheel speed is zero and the brake pedal is depressed (for automatic transmissions), or when the transmission is in neutral and the clutch pedal is released (for manual transmissions). Other considerations for determining when the engine should be shut down may include the engine coolant temperature, battery state of charge (SOC), fuel rail pressure, A/C operation, and other considerations that may be used to prevent an engine shut down and/or to initiate an engine restart.
In some markets where assisted direct start, ADS, or stop/start (S/S) systems will soon be common for example, in European markets) active suspension systems (e.g. full hydro-pneumatic suspension systems with actuators at each wheel and/or roll control systems with front and/or rear actuation) are becoming increasingly popular. However, because the power required for operating the active suspension system comes from the engine, shutdown of the engine during S/S engine shutdown events may impair or prevent operation of elements of the suspension system at a time when the suspension is needed for optimum vehicle control. This is especially the case for rolling stop/start (RSS) events that occur when the operator is not depressing the accelerator pedal and the vehicle speed is below a threshold, typically a value greater than “zero” (for example, 60 KPH).
Therefore, in vehicles incorporating both ADS and active suspension systems, a need exists for some method of integrating the two systems to help ensure that active suspension, system operation is not compromised during RSS or S/S engine shutdown events.